Numerous approaches to the separation of a gas from a mixture of gases by differential permeation have been investigated. Robb, et al., in U.S. Pat. No. 3,335,545, have proposed use of a liquid, entrapped in a porous or permeable support, to separate mixtures of gases. The use of a so-called "quasi-liquid film" for example, diethylene glycol, in a support has permitted separation of carbon dioxide from nitrogen, hydrogen or oxygen, the selectivity being somewhat higher than would be predicted on the basis of the molecular weights of the gases as the sole factor influencng separation. Ward, III, has proposed, in U.S. Pat. No. 3,503,186, a similar procedure for separating sulfur dioxide from other gases.
The use of facilitated transport liquid membranes has been reviewed by Way, et al., J. Membrane Science, vol. 12 (1982), pages 239-259. Another typical disclosure of gas separation using a facilitated transport immobilized membrane is that of Bassett, at al., Biochemica et Biophysica Acta, vol 211 (1970), pages 194-215. Facilitated transport of gases through liquid membranes is also recited for example, in the following U.S. Patents:
______________________________________ 3,396,510 Ward, III, et al. 3,676,220 Ward, III 3,819,806 Ward, III, et al. 4,014,665 Steigelmann 4,015,955 Steigelmann, et al. 4,119,408 Matson 4,147,754 Ward, III 4,174,374 Matson ______________________________________
Ward, III, et al. U.S. Pat. No. 3,396,510 recite using an immobilized liquid film as a permeable membrane, wherein the liquid film contains at least one soluble, non-volatile, dissolved carrier species, which is reversibly chemically reactive with a selected component of a gaseous mixture.
Ward, III, et al. U.S. Pat. No. 3,819,806 discloses the formation of an immobilized liquid membrane for the separation of an acid gas from other components of a gas stream. Transport of the acid gas through the immobilized liqud membrane is facilitated by the addition of a water-soluble salt to the liquid membrane.
Steigelmann U.S. Pat. No. 4,014,665 discloses a membrane-liquid barrier system having a complex-forming, silver-containing ion component in an aqueous solution. The membrane-liquid barrier combination can be used to separate olefinically-unsaturated hydrocarbons from mixtures containing them and other components, such as alkanes.
Kmuria et al. (U.S. Pat. No. 4,318,714) have recited using an ion-exchange membrane to accomplish facilitated separation of a gas from a mixture of gases.
Yamamoto et al. (U.S Pat. No. 3,155,467) have disclosed separation and purification of hydrogen, using a palladium alloy as a permeable wall structure.
Solid and molten salt electrolytes have been disclosed, in the fuel cell or electrochemical arts, in the following representative patents:
______________________________________ 3,400,054 Ruka et al. 3,432,363 Gillis 3,527,618 Bushnell 3,727,058 Schrey 4,317,865 Trocciola et al. U.K. 2,082,156 Yoshisato et al. ______________________________________
A limiting feature in many of these disclosures is that a gas should not completely permeate the electrolyte or electrode, since complete penetration could short circuit the device.
Batigne et al.. U.S. Pat. No. 4,396,572. recite using a porous ceramic barrier, having a plurality of superimposed layers of pastes of varying composition, to separate uranium hexafluoride isotopes by ultrafiltration.
Fleck, U.S. Pat. No. 2,983,767, teaches separating a fluid mixture of organic compounds by passing the mixture over a diffusion barrier containing a specified Werner metal complex in the form of a crystalline solid which forms a clathrate inclusion compound with one or more components of the fluid.
Erickson, U.S. Pat. No. 4,132,766 teaches a process for separating oxygen from air by contacting the air with an oxygen acceptor comprised of a molten solution of alkali nitrite and nitrate salts at elevated temperature and pressure to react with the oxygen. The oxygen is subsequently recovered by reducing the pressure while supplying heat to the salt solution.
Trocciola. et al., U.S. Pat. No. 3,847,672 discloses a fuel cell system comprising a gas separator. The gas separator comprises a tile or block of salt in a molten or solid state having opposed reactive surfaces. A gas stream containing hydrogen and carbon dioxide is fed to one surface of the salt at which surface the CO.sub.2 is chemically taken up by the salt. A sweep or stripping gas is maintained at the downstream surface of the salt tile at which surface CO.sub.2 is released.
Dounoucos, U.S. Pat. No. 3,447,286 discloses a totally enclosed liquid membrane for the separation of gases. The membrane comprises a porous body having direct channels extending therethrough from face to face and providing an open area completely enclosed together with a selected liquid filling the channels between non-porous layers of solid permselective membrane material.
Pez, et al., U.S. Pat. No. 4,617,029 teaches a process for separating a gas from a mixture of gases by passing the gas mixture over a membrane selectively permeable by the gas being separated, owing to the occurrence of one or more reversible oxidation-reduction reactions between the gas being separated and a continuous layer of active molten material immobilized in a rigid, porous, inert support.